The present invention relates to a fluidized bed reactor and its use. More particularly, the present invention relates to a fluidized bed reactor having improved fluidization and a process for the catalytic oxidation of a hydrocarbon which comprises the reaction of a hydrocarbon with an oxygen containing gas in the presence of a catalyst in the fluidized bed reactor.
It is known that a fluidized bed reactor can be widely used for various reactions because of its excellent characteristics. In particular, a fluidized bed reactor makes the best use of a high cooling efficiency and can be operated even in an explosive composition range. For these reasons, the fluidized bed reactor finds a wide application in various oxidation reactions involving oxygen gas, e.g., catalytic oxidation of a hydrocarbon, particularly production of maleic anhydride by the oxidation of a hydrocarbon having four carbon atoms, or production of ethane dichloride by oxy-chlorination of ethylene.
In a fluidized bed reactor, the fluidization of a particulate material in the reactor has a great effect on the results of reaction (The particulate material is normally a catalyst and thus will be simply referred to as xe2x80x9ccatalystxe2x80x9d). It has been heretofore recognized important to minimize the size of bubbles in a fluidized bed reactor so that the catalyst and the gas can be kept in good contact. To this end, it has been practiced to design the shape of gas distributor so properly that the diameter of bubbles generated can be minimized. It has been also practiced to provide an internal unit in the fluidized bed reactor or raise the superficial gas velocity so that bubble breakage can be accelerated.
Further, JP-W-1-503211 proposes a fluidized bed reactor comprising at least one horizontal cooling coil provided in the interior thereof. It is described that this arrangement provides an improvement in the fluidization of the catalyst and thus allows a proper temperature control. However, this approach leaves something to be desired in the improvement of fluidization.
The present invention has been worked out for the purpose of providing a fluidized bed reactor which allows the catalyst to be fluidized more uniformly than ever and thus to give an easy control over the reaction.
The inventors made extensive studies of the foregoing problems. As a result, it was found that when the effective cross-sectional area of the dense-phase fluidized bed region of the catalyst in a fluidized bed reactor (region where the catalyst can flow) is within a predetermined range, the fluidization of the catalyst can be remarkably improved and the reaction yield is good. Thus, the present invention has been worked out.
In other words, the first essence of the present invention lies in a fluidized bed reactor comprising a cooling coil, a dummy pipe and/or a cyclone wherein the average cross-sectional area occupied by a cooling coil, a dummy pipe and/or a cyclone leg is 10% or more of the average cross-sectional area of said reactor in a dense-phase fluidized catalyst bed region.
In accordance with preferred embodiments of implication of the present invention, there are provided the foregoing reactor wherein the average cross-sectional area occuplied by the cooling coil, dummy pipe and/or cyclone leg is 25% or less of the average cross-sectional area of said reactor in said region; the foregoing reactor wherein the average cross-sectional area occuplied by the cooling coil, dummy pipe and/or cyclone leg is from 12 to 20% of the average cross-sectional area of said reactor in said region; the foregoing reactor comprising therein a catalyst containing fine particles having a mass mean particle diameter of from 30 to 100 xcexcm and a particle diameter of not more than 44 xcexcm in an amount of from 10 to 80% by weight, preferably from 20 to 70% by weight and having a particle density of not more than 5,000 kg/m3, preferably not more than 4,000 kg/m3; and the foregoing reactor wherein a particulate catalyst is kept fluidized by a gas supplied into the reactor at the lower portion thereof.
The second essence of the present invention lies in a process for the catalytic oxidation of a hydrocarbon which comprises the reaction of a hydrocarbon with an oxygen-containing gas in the presence of a catalyst in the fluidized bed reactor.
In accordance with a preferred embodiment of the present invention, there is provided the foregoing catalytic oxidation process wherein a hydrocarbon having four carbon atoms and a gas containing oxygen are reacted to produce maleic anhydride.